Rio Tinto Group, the world’s third-largest mining company, is nearing an agreement to buy a 49% stake in Alrosa’s Severalmaz diamond mine for $350 million, according to a person with knowledge of the talks, Bloomberg reported.

Rio’s production technology would help Alrosa extract diamonds from the mine’s low-grade ore, said the person, who declined to be identified because a deal is yet to be signed, the report said.

The addition of a strategic investor would allow Alrosa, the largest diamond miner by output, to boost efficiency at the mine, which yields as little as half a carat per metric ton of ore, compared with Alrosa’s normal yield of 5 to 7 carats, according to the company. For Rio, Severalmaz would help it revive its diamond production, which fell 1.3% last year, said the Bloomberg report.

“We are very, very close to a deal with an investor,” Alrosa Chief Executive Officer Fyodor Andreev said in a March 10 interview. “I am not ready to say now which companies.”

Tony Shaffer, a spokesman for London-based Rio, declined to comment.

Producers of rough diamonds have taken on costlier projects as older mines are depleted. Alrosa has sought a strategic investor in its unprofitable Severalmaz venture, which operates the Lomonosov diamond field in northern Russia, since last year, and in June gave Rio a tour of the mine. Severalmaz has $12 billion of diamond reserves, according to the unit’s website.

Alrosa’s output rose 4.7% last year to 34.3 million carats, the miner said in a statement on March 18.